Manufacture of fine edged blades



Nov. 15, 1932. T. H. FRosT MANUPACTURE 0F FINE EDGED BLADES Filed Jan.15, 1951 wat Mo 7471595 Patented: Nov. 15, 1932 UNITED STATES THOMAS H.FROST, OF CAMBRIDGE, MASSACHUSETTS MANUFACTUREOF FINE .EDGED BLADESapplication mea January 1s, 1931, serial No. 508,505.

This invention relates to improvements in the manufacture of fine edgedblades and blade strips of ferrous alloys which may be hardened by theprocess of nitriding, that is to say, by introducing nitrogen into. orcausing it to combine with the alloy. In one aspect my inventioncomprises a new and improved method of making such blades in strip form.In another aspect it comprises a novel apparatus herein shown asemployed in the pract-ice of the method of my invcntion. i

An important field of use of my invention is in the production of safetyrazor blades of the thin ilexible type which are adapted for use inholders wherein they are clamped for support In the nitriding operationasheretofore carried out ditliculty has been experienced in preservingthe shape of the blank in the nitrided and hardened blade on account ofthe fact that a local expansion of the material is likely to take placewhich tendsto warp or distort the blade to an objectionable extent.Blades nitrided through their entire area, particularly -thin flexibleedges only without the necessity of plating or otherwise coating thestrip preparatory to the nitriding operation. I have discovered thatthis may be accomplished bv subjecting a strip o'f ferrous nitridablealloy to the action of a nitriding agent within aheated strip to orabove that container and simultaneously cooling aselected area in thestrip to a temperature below that at which a nitri-ding action will takeplace, or preventing such areas from becoming heated to that degree. Forexample, in the case of certain' alloys a temperature of approximately950 F. is suiiicient to cause ammonia gas to nitride the exposed andheated portions, Whereas below that temperature little or no nitridingeffect can be detected. Accordingly I propose to maintain anintermediate zone in the blade blank or strip below the temperature of950 F. while heating the marginal portions of the y temperature. sult isthat the marginal portions of the strip will become fully nitrided andhardened, whereas the intermediate portion thereof will retain itsoriginal relatively soft and ductile characteristics.

The method of my invention is of particularadvantage in that it lendsitself to continuous-process operation and may therefore be carried outwith marked economy particularly in those cases where the material to betreated is available inlong strips or ribbons. Under these conditionsthe strip may be moved through a heated ammonia container provided witha cooling medium of less width than the blade strip which will beeffective to maintain the selected area in the strip below the criticaltemperature.

Another advantage of my improved meth- `od is that it may be carried outif desired upon a strip which is maintained under tension during itspassage through the heated container. This, as explained in my priorapplication Ser. No. 506,423 filed January 3, 1931, is one effectivemanner of obviating distortion in the blank during thenitridingoperation. From this standpoint the present invention consists in adevelopment or carrying forward of the principles disclosed in saidapplication with a view to increasing 'its field of use and economy ofoperation.

The re- 1.30

7hile the method of my invention may be practised with the assistance ofapparatus of various descriptions, I have herein disclosed one formwhich may be used with entire satisfaction and such apparatus isinclu-ded within the scope of the present invention. As herein shown,this apparatus comprises a heated container which may be charged with anitriding agent and in which is disposed an elongated cooling medium ofless width than the strip to be treated, disposed closely sul adjacentto the path of movement of the strip and being effective to cool or toprevent heating of that portion ofthe strip located opposite to it.Preferably the cooling medium is arrange-d for adjustment to and fromthe path of the blade blank or strip s o that its cooling effect may beregulated and the width of the unnitrided zone varied in accordance withthe requirements of the case.

I have found it effective to provide oppositely disposed water cooledducts between which the blade strip is arranged to be guided companyingdrawing in connection with the apparatus referred to and in which Fig. 1is a view in longitudinal section, somewhat diagrammatic in character,of the apparatus, showing the blade strip in the nitriding step.

Fig. 2 is a view on an enlarged scale of 2 2 of Fig; 1.

Fig. 3 is a view in perspective of a portion of the blade strip, and

Fig. 4 is a similar view of a finished blade.

In manufacturing safety razor blades by the method of my inventionherein illustrated the blade blanks 10 are first outlined in strip form.As shown in Fig. 3 this may be done by punching or dieing out suitableedge notches and perforations in a continuous strip or ribbon ofnitralloy or other nitridable the apparatus in cross section upon theline alloy which may be secured commercially,

rolled to the desired thickness. As herein shown each blade blank isprovided with an internal aperture 12 in the shape of slot intersectingrecesses, and with cut-out portions forming corner notches 14 which, inthe finished blade, obviate the possibility of corner pressure from thecap of the razor. The strip may be scored or otherwise marked to set offone'blank from the next, these steps and the step of rough grinding thestrip t0 form bevels 15 being carried out upon the material incontinuous strip form.

The material employed in the strip described above may be selected fromalloys of suitable analysis, such for example as either of thefollowing: i

Element Analysis A Analysis B Carbon .36 .23 Manganese 51 51 'con .27.20 Aluminum 1. 23 1.24 Chromium 1. 49 1. 58 Sulphur 010 011 PhosphorusL .013 .011 Molybdenum 18 l. 20

Having prepared the blade strip in the manner above outlined it is readyfor the nitriding operation which may be effectively carried out byapparatus which will now be described. `l

The apparatus comprises broadly an elongated heated chamber or furnacecharged with a nitriding agent, liquid-sealed at each end and providedwith guides for a tensioned bladestrip, together with an elongatedcooling medium arranged to act upon the strip as it is passed throughthe furnace. The'furnace comprises a horizontally disposed pi 20provided at either end. with a special tting or elbow 22 directeddownwardly at an angle of degrees. Each of the fittings 22 is providedwith an idle guide rod 24 disl posed so as to direct the blade strip,which as a whole is indicated by the reference character 16, in a pathcoinciding substantially with the longitudinal axis of the pipe 20.

The fitting 22 at the left or entering end of pipe 2O is provided witha. downwardly extending pipe 26 which, at its lower end is arranged toextend beneath the surface of oil 28 contained Vin a tank 30. The tank30 is provided upon opposite walls with parallel vertically dis osedAguide strips 32 in 4 which'is mounted a orizontal spindle 34 carrying'aroller 36 and having suspended from its ends a yoke 38 with a downwardlyextending stem upon which is supported a weight 40. The fitting 22 atthe right hand or discharging end of the furnace is provided with thedownwardly extending pipe 42 bevelled at its lower end and extendingbeneath oil '28 in a tank 44. The tank 44 is provided with journalbearings for 'a roll V46 which is maintained in a fixed positionentirely submerged by the oil.

The blade strip 16 is delivered to the roll 36 at the enterfng end ofthe apparatus from a pair of positively driven feed rolls 50 whichadvance the blade strip at a definite uniform rate. Upon leaving thetank 44at the delivering end of the apparatus the blade strip is fedbetween two similar positively driven feed rolls 52 which are operatedto deliver the blade strip from the apparatus at the same rate at whichit is delivered thereto.

The length of the strip maintained between the two sets of feed rollersis regulated so that the Weighted roll 36 will be at all times suspendedfrom it, and the entire blade strip between the feed rolls -will thus bemaintained under a uniformand controllable degree of tension. This maybe regulated, as may be apparent, by reducin or increasing the size ofthe wefght 40. he blade strlp is thus stretched tightly between the uiderolls 24 and in the portion of its pat betweenthese guide rolls and thefeed rolls at either end of the apparatus. Moreover, since the rolls areall of plain cylindrical shape the blade strip is flattened by itscontact with them.

The feeding and tensioning of the blade strip has now .been described.The heating thereof is effected in the apparatus illustrated byencircling the pipe 20 with a coil of resistance wire 54 embedded orcovered with insulating material 56. By the assage of an electriccurrent through this coil the pipe 20 may be .heated to any desiredtemperature and maintained uniformly thereat. A temperature of 950C. F.to 1400 F. for the interior of the pipe Q0 has been found satisfactoryinpractise and' permits the blade strip to be fed at a convenient rateof speed.

The heated pipe 20, together with the tittings 22, and the inclinedpfpes 46 and 42 constitute a fluid sealed container to which ammonia maybe supplied conveniently in the form of gas. As herein shown, ammonia isdelivered to the left hand pipe420 through a small pipe 58 leading intothe bottom thereof, and it is discharged from the apparatus through a,pipe 60 of similar size leading from the upper side thereof near therfht hand end. y

n order to protect the intermediate portion of the blade and maintain itat a temperature below that at which the nitriding operation will takeplace the pipe 20 is provided with a pair of longitudinally disposedducts and 66 substantially rectangular in cross section. The upper ductis adjustably supported in a position above the path of the blade strip16 by a pair of threaded stems 64. 62 in the pipe and through a packinggland 63 and each is provided at its outer end with a hand wheel. Theinner end of each stem makes a swivel connection with a cap plate 61secured to the upper surface of the duct 65, the constructi on beingsuch that by turning the threaded stems the duct 65 may be adjustedvertically at each end and thus caused to lie nearer to or further fromthe upper surface of the blade strip 16. The lower duct 66 is mountedfor adjustment by similarly threaded stems 64 beneath the blade strip.The two ducts 65 and 66 are connected at either end by a pair offlexible unions 67 which permit relative movement.

These extend outwardly through bosses Cooling water is supplied to theupper duct 65 through a supply pipe 68 and discharged at its oppositeend through a delivery pipe 71. The supply pipe 68 enters the left-handfitting. 22 through a gland 69 and the de livery pipe 70 leaves theright-hand fitting v 22 through a gland 71 constructed to permit aslight movement of the pipe when the duct is adjusted and tomaintain thev.whole container substantially gas-tight.

The cooling 'ducts 65 and `66 are of less width than the blade stripand,are located with respect to it'so' that Athe marginal portions onlyof the strip are vfully exposed to the heat of the furnace. Thisarrangement is best shown in Fig. 2 from which it will be plain thatlittle more of the blade strip than the bevelled portions projectlaterally beyond the sides of the cooling ducts. It will be seen thatthe blade strip is thus shielded in a wide intermediate zone from theheat of the furnace and byl adjusting the position of the cooling ductsand regulating the temperature and flow of the cooling waterit ispossible to maintain this portion of the strip at a temperature belowthat at which the nitriding can take place. The blade strip thereforeemerges from the apparatus with its body portion soft and ductile andwith its marginal edges nitrided to the desired degree.

The pipe 20 may be of any convenient harden the marginal edges of ablade strip f suiicient for the manufacture of razor blades.

It may be further noted that the novel method of my invention is ofparticular advantage from the standpoint of ammonia consumption in thatthe loss caused by dissociation of the ammonia due to contact withhighly heated 'surfaces is reduced to a minimum by the employment ofcooling mediums coextensive with the blade strip. l

Having completed the nitriding operation inthe manner above outlined,the blade strip may be subjected lto a final sharpening operation andmaythen b e cutor broken on the scored lines into its individualcomponent blades.

4While I have illustrated the method of my invention as being carriedout upon blade strips, it will be apparent that many of its steps areapplicableto blade blanks not necessarily in strip form.

Having thus described my invention what which consists in subjecting 'astrip of ferrous nitridable alloy to the action of ammonia, heatlng amarginal portion of the strip, and simultaneously maintaining aninterme- `diate portion thereof at a temperature below that at whichnitriding will take place.l

2. The method of making blade strip for use in the manufacture of fineedged blades, which consists ,in subjecting a strip of ferrousnitridable alloy to the action of ammonia, and

simultaneously heating a marginal portion of the strip to a temperatureabove 950 F. while maintaining an intermediate portion thereof belownitriding temperature.

3. The method of making blade strip for use in the manufacture of lineedged blades,

Iwhich consists in subjecting a strip of ferrous nitridable alloy to theaction ofa nitriding agent within a heated container, and simultaneouslycooling a selected area in the strip sufficiently to prevent a nitridingaction in said area.

4. The method of making blade strip for use in the manufacture of fineedged blades,

, which consists in passing a strip of nitridable ferrous allo through aheated container having a nitriding agent therein, and simultaneouslysubjecting less than the full width of the strip to the action of acooling medium to prevent nitriding therein.

5. The method of making blade strip for use in the manufacture of fineedged blades,

which consists in feeding a strip of nitrid-v able ferrous alloy througha heated and ammonia-charged container, and simultaneously cooling theopposite faces'of the strip between its margins in selected areas to a.temperature below that at which nitriding takes place.

6. The method of making blade strip for use in the manufacture of lineedged blades, which consists in feeding a strip of nitridable ferrousalloy through a Vheated `and ammonia-charged container, maintaining thestrip under tension, and at the same time cooling an intermediate zonetherein below nitriding temperature.

7. The method of making blade strip for use in the manufacture of fineedged blades, which consists inpassing a strip of nitridable ferrousalloy through an atmosphere of ammonia heated to a temperaturesufficient to effect in the alloy a nitriding operation, andsimultanously maintaining a se ected area of the strip below suchcritical temperature.

8. The methodof makin blade stri for use-in the manufacture of e edgedbiiides, which consists in subjecting a. beveled-edged strip of ferrousnitridable alloy to the action of a nitriding agent withinv a. heatedcontainer, and simultaneously embracing the body of the strip betweenoppositely disposed no i

